feat: Implement Issue #1 - Database initialization and front matter parsing

Complete TDD implementation of core MarkiTect functionality:

**Database Module (markitect/database.py):**
- DatabaseManager class with SQLite database initialization
- markdown_files table with proper schema (id, filename, front_matter, content, created_at)
- Front matter storage as JSON with content separation
- File storage, retrieval, and listing methods
- Comprehensive error handling

**Front Matter Module (markitect/frontmatter.py):**
- FrontMatterParser class with YAML front matter parsing
- Clean separation of metadata from markdown content
- Graceful handling of invalid YAML and missing front matter
- Regex-based parsing with proper delimiter handling

**Dependencies:**
- Added PyYAML for front matter parsing
- Updated pyproject.toml with new dependency

**Test Coverage:**
- 9 comprehensive tests covering all functionality
- Database initialization and schema validation
- Front matter parsing with Issue #1 example content
- Integrated workflow testing (storage/retrieval)
- Error handling for edge cases

**TDD Process:**
- RED phase: 8 failing tests defining requirements
- GREEN phase: Minimal implementation making all tests pass
- Validation: Complete workflow verified with example content

This implementation provides the foundation for all subsequent MarkiTect
features, handling the exact example from Issue #1 specification.

Issue #1: Initialize Database and Store Example Markdown File
coulomb/markitect_project#1

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -8,7 +8,7 @@ version = "0.1.0"
 description = "Advanced Markdown engine for structured content"
 readme = "README.md"
 requires-python = ">=3.8"
-dependencies = ["markdown-it-py"]
+dependencies = ["markdown-it-py", "PyYAML"]
 
 [tool.setuptools.packages.find]
 include = ["markitect*"]